How not to mulch around a tree
Unfortunately mulching around a tree is not heaping piles of mulch up and around the trunk. Mulching is not creating a volcanic cone of mulch right up against the trunk.
Just applying mulch onto the trunk of the tree will result in a shortened life expectancy, or even death of the tree. Mulch that touches the trunk is moist from rainfall and irrigation. Over time this moisture will rot and decay the bark layer which effects the layer area of tree growth and eventually rots the heartwood of the tree. Deep piles of mulch, over 4 to 6 inches deep will also exclude oxygen from the soil. This results in root development up into the mulch layer, not down into the soil. These so called surface or mulch roots do little to support the tree in the long-term for robust growth